This invention relates to optical brighteners, and more particularly relates to a fluorescent compound formed by reacting at least one aminofunctional organosilicon compound with at least one optical brightener having the formula ##STR2## and wherein R denotes anilino, sulfanilic acid, metanilic acid, or anilin-2,5-disulfonic acid, and R' is methoxy, methylamino, N-methyl-N-hydroxyethylamino, bis(hydroxyethyl)amino, morpholino, anilino, or diethylamino.
Brightening is concerned with the preparation of fabrics whose commercial value is dependent on the highest possible whiteness or brightness. It is well known that many substrates possess a yellow cast which may be eliminated by means of blue or blue-violet light. Optical brighteners, termed fluorescent whitening and fluorescent brightening agents, compensate for the yellow cast. Yellow cast is produced by the absorption of short-wavelength light in the violet-to-blue portion of the spectrum. Optical brighteners replace in part this short-wavelength light and a complete white is attained. The brightener produces additional light by means of fluorescence. It absorbs the invisible ultraviolet portion of the daylight spectrum and converts the energy into the longer-wavelength visible portion of the spectrum which is blue to blue-violet light. Thus, an optical brightener absorbs ultraviolet light and remits it in the blue region of the visible spectrum. The human eye is sensitive to a narrow band of radiant energy. However, it is not sensitive to ultraviolet or infrared wavelengths. Therefore, the eye does not respond to all of the radiation from a white surface upon which sunlight is falling. Most of the light is reflected and only radiation in the range of 400 to about 800 mu is sensed by the eye. Optical brighteners do not significantly affect the total radiation reflected by the fabric, however, they do convert absorbed invisible ultraviolet radiation into visible light making the fabric appear whiter and brighter.
The prior art is replete with compounds described as fluorescent, however, only some of these compounds include silicon. For example, in U.S. Pat. No. 4,595,599, issued June 17, 1986, there is described a luminescent compound that is a silane and having incorporated therein cyanine, xanthene, and anthracene, type dye structure moieties. The compounds are said to be useful as highway and roadway markings. In contrast, the compositions of the present invention are aminoalkylfunctional organosilicon compounds, however, the incorporated moiety is an optical brightener with aldehyde or sulfonic acid type functional groupings. The compositions disclosed herein are further useful as additives to laundry detergents and hair dyes. U.S. Pat. No. 3,427,273, issued Feb. 11, 1969, relates to organopolysiloxane compounds that are prepared by the hydrolysis of silanes and are rendered fluorescent by bonding a polynuclear aromatic hydrocarbon substituent directly to the silicon. The compositions are stated to be useful as signs, markers, and dials. While the present invention includes polysiloxanes that are rendered fluorescent, they differ substantially from the compounds in the 273' patent, in that, they are aminoalkylfunctional-type polysiloxanes, and they are rendered fluorescent by bonding an optical brightener substituent having aldehyde or sulfonic acid type functional groupings to the siloxane molecule. As noted above, the compounds of the present invention are useful as additives in laundry detergents and hair dyes. Thus, there is provided herein new categories of fluorescent compositions not known in the prior art.